In the field of rotorcraft, helicopters, or the like, it is common practice to drive a rotor by means of a plurality of engine members, in particular a pair of engine members. The number of such engine members is nevertheless not limiting on the scope of the present invention.
The rotors of a helicopter are driven by engine members via one or more reduction stages that present a constant reduction ratio. This applies to driving the rotary wing, or more precisely the blades.
In the state of the art, systems are known in which one or more speeds of rotation for rotors are accessible for a given speed of rotation for the engine member(s). In order to obtain such a variation in the speed of the rotor, such systems require a corresponding modification to be made to the speed of rotation of the engine member(s), and that generally leads to a temporary loss of torque and power.
Varying the speed of rotation of a known helicopter rotor thus results from causing the speed of rotation of the engine members to vary in a corresponding manner. It is found to be impossible to obtain a large speed difference without loss of torque transmission from the engine members. This constitutes a drawback that is not negligible whether in terms of performance or in terms of safety in the operation of helicopters.
By way of example, document US 2006/0 269 414 discloses a device enabling a variable speed main gearbox to be made that includes freewheels and clutches. Nevertheless, such devices suffer from a certain number of drawbacks. Because of overrunning of their component plates that come into mutual contact, the clutches do not enable the power delivered by an engine member to be transmitted instantaneously. There thus results an instant in which the system for transmitting speed of rotation to the main gearbox (MGB) is interrupted, and the torque that is transmitted is then zero. In addition, the clutches suffer from problems of wear and/or adjustment, that can be harmful to the reliability and the efficiency of devices in which they are incorporated.